1. Field of the Invention
This invention relates generally to the field of chemical reactions. More specifically, the invention relates to methods of making diester phthalates incorporating high shear mixing.
2. Background of the Invention
Plasticizers are widely used in many ways in plastics, coating compositions, sealing compositions and rubber articles. They interact physically with thermoplastic high polymers without reacting chemically, preferably by means of their solvent and swelling capability. This forms a homogeneous system whose thermoplastic range has been shifted to lower temperatures compared to the original polymer, with the result that, for example, the ability to change shape and the elasticity are increased and the hardness is reduced.
To open up very wide fields of application for plasticizers, they have to fulfill a number of requirements. In the ideal case, they should be odorless, colorless, light-resistant, cold-resistant and heat-resistant. In addition, it is expected that they are resistant to water, do not burn readily, have a low volatility and are not harmful to health. Furthermore, the preparation of the plasticizers should be simple and, to meet ecological demands, should be carried out without producing waste materials such as by-products which cannot be recycled and wastewater containing pollutants.
Among the most important plasticizers are the esters of dicarboxylic and polycarboxylic acids with plasticizer alcohols, i.e. unbranched or branched primary alcohols having from about 6 to 13 carbon atoms, which can be used as individual compounds or as a mixture. The preparation of the esters has been carried out by the classical process by reacting the acids or acid anhydrides with an alcohol or a mixture of different alcohols in the presence of an acid, preferably sulfuric acid, as catalyst. The alcohol component is usually used in excess. Attempts have been made to counter adverse color and odor of the reaction product by targeted selection of the acid used as catalyst, by mild reaction conditions and by complicated purification measures.
A further development in the preparation of esters suitable as plasticizers constitutes the use of metal-containing esterification catalysts. Suitable catalysts are, for example, tin, titanium and zirconium which are used as finely divided metals or advantageously in the form of their salts, oxides or soluble organic compounds. These catalysts are high-temperature catalysts which reach their full activity only at esterification temperatures above 180° C. Examples are tin powder, tin(II) oxide, tin(II) oxalate, titanate esters such as tetraisopropyl orthotitanate or tetrabutyl orthotitanate and also zirconium esters such as tetrabutyl zirconate. Alkyl titanates and titanium chelates, i.e. titanates of polyalcohols, have achieved particular importance in industrial production processes.
Furthermore, another process for the esterification of phthalic anhydride involves reaction with isodecanol in the presence of tetrabutyl titanate as catalyst at 230° C. Subsequent to the esterification, the reaction mixture is treated with sodium carbonate solution and the excess alcohol is distilled off. The treatment with the sodium carbonate solution neutralizes the phthalic monoesters present in the reaction mixture to form the corresponding salts. These salts are obtained as a slimy precipitate which can be filtered off only with difficulty, necessitating a high outlay in terms of time and apparatus. Obtaining the desired phthalic diester in pure form is thus associated with considerable difficulties. The modern processes for preparing ester plasticizers thus do not yet fulfill all aspects of the above-described demands made of the production process and the reaction product.
Consequently, there is a need for accelerated methods for esterification by improving the mixing of alcohol into the phthalic acid derivative phase.